The anxiety felt by one when they think that there isn't enough fuel in their gas tank to complete a trip.
Tankxiety is known to be accompanied by anger and a sense of false security after thinking that one is safe. (See example.)
The terminology comes from a portmanteau of the words "Tank" and Anxiety."
Frank - "Fuck, fuck, fuck, FUCK!"
Mitch - "What is it dude?"
Frank - "The fuel needle is under a quarter! I'm coming down with a case of tankxiety! SHIT! What if we run out of gas on the 401? SHIT! Oh no, the anger is setting in! GOD DAMN HONDA! FUCK YOU!"
Mitch - "Don't panic, dude!"
Frank - "Yeah. Yeah! Uh, maybe you're right!"